Acoustic echo cancellation (AEC) is used in telecommunications devices to improve audio quality. In this environment, an echo is a delayed reoccurrence of an original signal in a received or retransmitted signal.
Audio echo may be caused by an acoustic path between the microphone and speaker of a communications device such as a telephone handset. AEC is particularly useful in so-called “hands-free” communications devices, where there is very little acoustic isolation between the microphone and speaker of the device.
AEC is typically performed by recognizing the original audio and subtracting it from the signal in which it reappears as an echo. This function may be performed by an adaptive linear filter, such as an adaptive finite impulse response (FIR) filter. An adaptive filter has weights or coefficients that are dynamically optimized to minimize the presence of echo audio in a signal.
In practice, a residual echo typically remains after application of an adaptive filter. This may be due to insufficient length of the adaptive filter, non-linearities in the acoustic echo path, and/or imperfections in echo modeling. Additional filtering and/or processing may therefore be performed in certain situations to reduce residual echo.
Audio signals may also be processed to reduce noise, which may include environmental background audio as well as noise introduced by telecommunications devices and systems themselves.